基于砂岩蠕变试验的非线性蠕变模型辨识研究

Study on Identification of Nonlinear Creep Model Based on Creep Tests of Sandstone

为了研究砂岩的蠕变特性,利用全自动三轴伺服仪对砂岩试样进行10 MPa围压下的常规三轴试验和蠕变试验。为有效描述蠕变全过程,提出了一种含分数阶导数的非线性蠕变模型并进行验证。结果表明:在蠕变衰减、稳定阶段,试样环向蠕变速率和轴向蠕变速率比较接近;在蠕变加速阶段,试样的蠕变速率迅速增大,环向较轴向先发生加速蠕变,且环向加速蠕变速率更大,稳定蠕变速率随着应力水平的增大而增大,环向稳定蠕变速率增幅较轴向大,可见环向蠕变速率受应力水平影响更大,建立的含分数阶导数的非线性蠕变模型能较好模拟蠕变全过程,具有较高的准确性。

In order to study the creep characteristics of sandstone,the conventional triaxial and creep experiments of the sample under 10 MPa confining pressures were carried out by using the full-automatic triaxial servo.On this basis,in order to simulate the whole creep process effectively,a nonlinear creep model with fractional derivatives is proposed and verified.The results show that the cyclic creep rate and axial creep rate of the specimens are close at the creep attenuation and stabilization stage.In the creep acceleration stage,the creep speed of the sample increases sharply.The accelerated creep occurs in the annular direction before in the axial direction,and the cyclic acceleration creep rate is higher.In addition,it was found that the steady-state creep speed increased with the increase of stress level,and the annular steady creep speed increased more quickly than the axial creep speed,suggesting that the annular creep speed was much more affected by stress level.The non-linear creep model with fractional derivative established in this paper can simulate the whole creep process well and has high accuracy.